1. Field of the Invention
The present invention relates to a vapor gas discharging apparatus for a hybrid electric vehicle (HEV), and more particularly, to a vapor gas discharging apparatus for an HEV, which is capable of stably discharging vapor gas inside a fuel tank during a motor operation period, even in a low-temperature environment.
2. Description of Related Art
In general, an important factor which is most considered in a fuel system when designing an HEV using an engine and a motor is how to discharge vapor gas, discharged from a fuel tank during an engine stop period, to the outside.
When the engine of the HEV is operated, vapor gas is transferred to the engine from a canister by a gasoline engine together with fuel.
That is, the HEV is driven by the motor in a middle/low-speed state and an idle state. At this time, since the engine is stopped, a purge rate of vapor gas introduced from the canister to the engine becomes zero. However, the fuel inside the fuel tank continuously discharges vapor gas. Therefore, when the vapor gas introduced into the canister from the fuel tank is not discharged to a purge line, the vapor gas is discharged to the atmosphere through an air outlet.
Therefore, the HEV may not meet the exhaust gas regulations, and may cause a problem in merchantability, such as smell.
In order to solve the above-described problem, a vapor gas discharging apparatus for an HEV has been proposed in the related art as illustrated in FIG. 1. The vapor gas discharging apparatus for an HEV includes a fuel tank 10 formed of a high-tension steel plate having such a large thickness as to endure excessive pressure of vapor gas, a vent valve 40 mounted on a vapor line 30 provided between fuel tank 10 and a canister 20, and a pressurized OBD valve 50 mounted at an outlet nipple 21 of canister 20.
In the vapor gas discharging apparatus for an HEV according to the related art, when there is no purge during a motor operation, a vapor gas flow is formed as follows.
In the vapor gas discharging apparatus for an HEV according to the related art, the engine is stopped during an idle or low-speed period, and vent valve 40 of vapor line 30 is blocked when the motor is operated. Accordingly, the vapor gas inside fuel tank 10 is not introduced into canister 20, but the vapor gas stays inside the fuel tank 10.
When the engine is operated during an acceleration period, vent valve 40 of vapor line 30 is opened. At this time, the vapor gas inside fuel tank 10 is introduced to canister 20 through vapor line 30, and then transferred to the engine along a purge line 60 connected to canister 20.
Meanwhile, the vapor gas discharging apparatus for an HEV according to the related art includes a heat storage material inside canister 20, in order to fundamentally prevent the vapor gas from being discharged to the atmosphere during the motor operation. Such a heat storage material repeats liquid/solid phase changes at a predetermined temperature, and emits latent heat during the phase change from liquid to solid. That is, hexadecane used as the heat storage material causes phase change at a reference temperature (about 18° C.) of the room temperature regulation. The latent heat generated at this time increases the internal temperature of canister 20, thereby increasing the desorption efficiency of activated carbon for collecting the vapor gas.
However, the production cost and weight of the vapor gas discharging apparatus may rise due to the heat storage material and the structure thereof, and the heat storage material may obtain an effect of the phase change only at the reference temperature. Therefore, the heat storage material does not have an effect upon an efficiency increase of canister 20 at a low temperature. Accordingly, there are difficulties in operating the vapor gas discharging apparatus in cold places and during the winter season.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.